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1 March 2005 AN EVALUATION OF TWO TRACERS IN SURFACE-FLOW WETLANDS: RHODAMINE-WT AND LITHIUM
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Abstract

Rhodamine-WT and LiCl were compared for their suitability as hydraulic tracers in wetlands. Using outdoor mesocosms, we found lithium to be more conservative than rhodamine-WT when initial concentrations were 4.9 to 64 μg/L for rhodamine-WT and 28–516 μg/L for Li (1:6 to 1:8 (wt/wt) ratio of rhodamine-WT to Li ). At higher initial concentrations (i.e., 100 μg/L for rhodamine-WT and 1000 μg/L for Li ), both tracers returned more than 95% of the injected amount in submerged aquatic vegetation-dominated mesocosms; rhodamine-WT was returned at only 74–75% in cattail-dominated mesocosms. Batch studies using different sediment substrates exposed to direct sunlight and shade indicated that Li was less affected by adsorption and microbial processes than was rhodamine-WT at low initial tracer concentrations of each (4.9 and 19.4 μg/L for rhodamine-WT and 28 and 106 μg/L for Li ). Both rhodamine-WT and Li desorb back to the water column in small amounts. The extent of adsorption losses by rhodamine-WT depended on the organic matter content of the sediment and the extent of photolysis. Even though rhodamine-WT was not as stable as LiCl at initial concentrations less than 60 μg/L, the reduction in the recoveries did not affect the accuracy of key hydraulic parameters (hydraulic retention time, dispersion, tanks-in-series, and wetland dispersion numbers) derived from the method of moments analysis as long as a discernible concentration-time response still existed. This is because the tracer losses were approximately zero-order and irreversible.

Forrest E. Dierberg and Thomas A. DeBusk "AN EVALUATION OF TWO TRACERS IN SURFACE-FLOW WETLANDS: RHODAMINE-WT AND LITHIUM," Wetlands 25(1), 8-25, (1 March 2005). https://doi.org/10.1672/0277-5212(2005)025[0008:AEOTTI]2.0.CO;2
Received: 19 September 2002; Accepted: 1 August 2004; Published: 1 March 2005
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